1. Field
The present invention relates to generating subcarrier signals for transmission in a frequency range between adjacent ultra-high frequency (UHF) channels. More particularly, the present invention relates to generating radio-frequency subcarrier signals by mixing input signals with local oscillator signals, each input signal including information to be transmitted by one of the RF subcarrier signals.
2. Description of the Related Art
In the field of wireless communications, the availability of bandwidth within the frequency spectrum becomes more restricted as more wireless technologies and services are introduced. To cope with the increasingly crowded spectrum, in recent years there has been interest in releasing previously reserved bandwidth between existing channels. In television (TV) broadcasting, this is referred to as TV White Space (TVWS).
It would be preferred if multiple services could be provided in the space between two channels, in order to maximise the usage of the available bandwidth. However, when subcarriers are used to provide a plurality of services in the narrow bandwidth between existing channels, the frequencies used for the subcarriers have to be accurately controlled to ensure that they do not interfere with the closely adjacent channels. Accordingly, there is a need to efficiently and cost-effectively generate subcarriers at well-defined frequencies for transmission in the TVWS between existing channels.